The invention relates to a device for detecting the position of an object, which device comprises a radiation source and a beam-splitting prism for reflecting the radiation emitted by the source to a radiation-sensitive detection system. The system comprises a plurality of detectors, the radiation distribution among the detectors being dependent on the position of the object relative to the radiation beam emitted by the source, and the outputs of the detectors being connected to an electronic circuit for producing an electric signal which provides an indication about the position of the object.
The beam-splitting prism is defined as a prism having two inclined surfaces which define a beam receiving edge of said prism.
U.S. Pat. No. 2,703,505 describes a device for aligning two parts of a machine relative to each other, a beam-splitting prism being arranged on one of said parts. Said prism receives a beam emitted by a radiation source and reflects the radiation to two radiation-sensitive detectors arranged on both sides of the prism. The output signals of the detectors are applied to an electronic circuit in the form of a Wheatstone bridge, whose output signal is a measure of the displacement of the one machine part relative to the other in a direction transverse to the main ray of the beam.
In the known device the radiation-sensitive detectors, in the form of phototubes, and the prism are always arranged on the same machine part. In a first embodiment of this device the radiation source is arranged on the one part and the prism with the detectors on the other part. Electrical wires must be connected, the wires of at least one part being arranged so as to move with said part. This is obviated by a second embodiment in which the radiation source and the prism with the detectors are arranged on the same machine part. However, in that case an additional reflector, which reflects the be beam parallel to itself, is arranged on the second machine part. For detecting the position of a small and light object the use of said reflector, which is relatively heavy and large, may pose a problem.
The known device only permits the measurement of rectilinear movements in two orthogonal directions.